Blog post

Sometimes teachers talk about physics in Lindy Hop classes and I never know how serious it is. Is it just a metaphor or there is something real about it. An article in The Guardian claims that dance=physics.

The title is “The science and magic of Lindy Hop”. In particular, it says

“Great partner dancers may not know it but they are masters of space, time and Newton’s laws of motion”
“When Fred Astaire and Ginger Rogers danced cheek-to-cheek in a close turn their two bodies achieved a beautiful line impossible for any individual. Dancing like this is a conversation in physics, where the bodies of both dancers are required to master the forces involved. In close hold, bodies are joined at the hip and hand. The follow exerts an equal and opposite force through arms and body in response to the lead. These equal and opposite forces, in accordance with Newton’s Third Law of Motion, allow the follow to dance in synchrony with the lead: as a mirror image. This symmetry can only be broken if the pairs of forces become unbalanced, causing one or both of the dancers to accelerate away from the other. For example, the lead may provide a subtle signal indicating to the follow to reduce the resistance, accept the transfer of momentum, and move away into a backwards step.
This, and all forces, cause a transfer of momentum (which is the product of mass and velocity). So, when the lead applies a net force, momentum is transferred to the follow. The more of the lead’s mass (body) moves as the force is applied, the greater the transfer of momentum and so the more the follow’s mass will move. Also, the longer it takes to transfer that momentum the smoother the ride. This is the difference between the slow gentle acceleration and deceleration of a careful driver, and the painful jarring of rapid acceleration or an emergency stop. The constant contact and gentle tension between the bodies of dancers means that momentum can be transferred at any time and over any time period.
This is beauty of partner dancing. When dancing alone you are constrained by your abilities and by the physical reality of friction and gravity. These forces are reliable, adaptable and predictable, but unchanging. When dancing with a partner these forces are countered by two different minds and bodies, each with its own interpretations, motivation, timing, strength and style.”

So, what is nice about science, is that you don’t have to believe everything other people say. Three physicists tried to test the hypothesis that good dancers optimize their Lindy Circle better than bad dancers in the article “Optimization and Pose Selection for a Lindy Hop Partnered Spin”.

“Swing dancers often talk about using the laws of
physics in performing their physically rigorous jumps, lifts, and
spins. Do expert swing dancers physically optimize their pose
for a partnered spin?”
“We did not find a difference between the fraction of optimality
achieved by beginners and expert dancers. The rotational
acceleration achieved by the dancers was roughly a factor
of ten less than the predicted optimal acceleration.”

So, maybe dance=physics, but so far there is no evidence that this is the case.